THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Status
Current state: Under Discussion Accepted
Discussion thread: here
JIRA: KAFKA-4481
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The same reasoning applies to the key, value and result types defined in methods that take Aggregator, StreamPartitioner, KeyValueMapper, ValueMapper, ProcessorSupplier, TransformerSupplier, ValueTransformerSupplier, ForeachAction, StreamPartitioner, and ValueJoiner.
Public Interfaces
| Affected methods | Current argument type | New argument type |
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(KGroupedStream|KGroupedTable).aggregate |
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(KTable|KStream).filter*, KStream.branch | Predicate<K, V> | Predicate<? super K, ? super V> |
(KStream|KTable).groupBy |
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KStream.(selectKey|map|flatMap), KTable.toStream | KeyValueMapper<K, V, X> | KeyValueMapper<? super K, ? super V, ? extends X> |
(KStream|KTable).mapValues, KStream.flatMapValues | ValueMapper<V, X> | ValueMapper<? super V, ? extends X> |
KStream.transform | TransformerSupplier<K, V, X> | TransformerSupplier<? super K, ? super V, ? extends X> |
| ValueTransformerSupplier<V, X> | ValueTransformerSupplier<? super V, ? extends X> |
(KStream|Ktable).foreach | ForeachAction<K, V> | ForeachAction<? super K, ? super V> |
| ProcessorSupplier<K, V> | ProcessorSupplier<? super K, ? super V> |
(KStream|KTable).*join | ValueJoiner<K, V, R> | ValueJoiner<? super K, ? super V, ? extends R> |
| StreamPartitioner<K, V> | StreamPartitioner<? super K, ? super V> |
KafkaStreams.metadataForKey | StreamPartitioner<K, V> | StreamPartitioner<? super K, ? super V> |
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- This change is binary compatible
- This change is source compatible for anyone merely calling the existing APIs
- This change is not source compatible for anyone extending the affected classes / interfaces.
- Update (2017-01-18): This change is not source compatible for anyone calling the Kafka Streams API from Scala due to differences in how Scala infers types.
Rejected Alternatives
For the aggregate and groupBy case the following alternatives would have been more correct – if we could drop support for Java 7 – since they would enforce the same type for initializer, serializer, and serde.
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Once we drop support for 1.7 we can always decide to switch to approach 2. without breaking source compatibility, by making a proposal similar to this KIP.
Notes
Update 2017-01-18: In light of
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TransformerSupplier and ValueTransformerSupplier